Workaround pip install failure
    
    While running tests on Fedora 26 with python3.6, it fails to install
    m2crypto < 0.27 due to swig error, this is a bug fixed in m2crypto 0.27,
    we need a temp workaround to get rid of the error before m2crypto
    release a new version to fix the blocker bug in 0.27:
    
    https://gitlab.com/m2crypto/m2crypto/commit/405d14ab7396ba570ecb68cc5cec52dc11424f27